This invention relates to electrical machines having centrally disposed stators and, in particular, to liquid-cooled alternators having centrally disposed stators.
Liquid-cooled generators, particularly alternators, are well known in the prior art. Many of the units are relatively large and complicated. It would be desirable to provide liquid-cooled generators or alternators for much smaller applications.
It is often of importance to obtain the highest possible efficiency when generating electricity by capturing and utilizing energy losses which occur during the process. In the case of a conventional generator, these losses are mostly waste heat which are usually vented out of the generator by means of a blower.
Such a blower draws in dirt and debris which are detrimental to the life of the bearings of the generator and may cause a fire in the generator. The air stream also carries noise from the engine-generator assembly. This noise may be difficult to dampen without disturbing the air stream or significantly increasing the size of the enclosure of the generator sets to allow for sound traps.
Liquid-cooled generators have been suggested in the past, for example in U.S. Pat. No. 6,046,520 to Betsch et al. In this example a conventional generator is surrounded by a housing and a liquid coolant is circulated in a space between the housing and the generator. The bulk of the generator is increased by the presence of the housing and water tightness of the generator is required.
Another liquid-cooled electrical machine is disclosed in U.S. Pat. No. 6,072,253 to Harpenau. As is typical of generators, the stator is on the outside and has cooling tubes connected thereto. The provision for cooling in the stator and the connections for the coolant increase the size of the machine.
Another such generator is disclosed in U.S. Pat. No. 6,160,332 to Tsuruhara. In this example a brushless generator has magnets on the centrally disposed rotor. The cooling chamber again is on the outside and extends about the exterior stator.
Despite the prior art, there is still a significant need for a compact liquid-cooled generator where the design is simple enough to minimize the cost of manufacture and, accordingly, the sale price.
It is an object of the invention to provide an improved electrical machine which is simple and compact and yet provides the benefits of liquid-cooling.
It is another object of the invention to provide a generator which can operate without bearings.
It is a still further object of the invention to provide an improved generator which has fewer parts than a conventional generator and requires less precision during manufacture and assembly.